Copying this object is disabled.
A postblit is present on this object, but not explicitly documented in the source.
Trusted on the assumption that byKey is @safe _enough_.
Add a mapping to a concrete file.
Create an in-memory file.
Release all resources held by the VFS.
File layer abstracting the handling of in-memory files and concrete filesystem files.
This struct abstracts and contains those differences.
The lookup rule for a filename is: - in-memory container. - load from the filesystem.
TODO Is it better to have everything as MMF? I think it would be possible to have the source code as an anonymous MMF.